1. Field of the Invention:
The present invention relates to a radiation-sensitive semiconductor device comprising a semiconductor body which at its surface has distinct radiation-sensitive diodes, and the invention relates in particular to a high resolution semiconductor line imager.
2. Description of the Related Art:
Radiation-sensitive semidconductor devices of the above-mentioned kind are used, for example, in photosensitive circuits for track following or positioning of light beams, and in image scanners wherein an image is line-wise scanned by means of a device comprising a great plurality of line-wise arranged photo-diodes that cover the width of the image to be scanned. In these semiconductor devices, the minority charge carriers that are generated in the diodes upon exposure to radiation produce corresponding voltages that form the output signal of the device.
There exists a problem in these devices in achieving effective mutual isolation of signal charges generated in adjacent diodes. As a matter of fact, the thus generated minority charge carriers must be confined in the lateral direction, i.e. in the direction of one diode towards an adjacent diode, in order to avoid cross-talk between adjacent diodes.
One technique for solving the problem comprises providing a sufficiently large spatial separation between the diodes and the associated depletion regions so that charge carriers which are generated in or near the depletion region of a particular diode do not contribute to the photoelectric current through an adjacent diode. However, such a spatial separation is at the sacrifice of the resolving power of the device.
In the FR Pat. Publication No. 2,367,353 there is disclosed a radiation sensitive line imager that comprises a multiplicity of line-wise arranged photodiodes that are formed by the suitable doping of local areas of a semi-conductor surface. The areas are electrically insulated from each other by oppositely doped intervening areas. These intervening oppositely doped areas make it necessary to increase the distance between the photo-sensitive areas, and they also increase the costprice of the manufacturing process of the device.
A radiation-sensitive device in which the distance between adjacent photodiodes can be very small (of the order of a few microns) while the cross-talk is low, is disclosed in GB-A No. 2,080,026. This application discloses a radiation-sensitive semiconductor device comprising a semiconductor body which at a flat surface has a radiation-sensitive diode having two or more sub-elements, in which device depletion regions associated with the sub-elements are formed on applying a reverse voltage across the sub-elements. At least one of the sub-elements has a connection for deriving a signal indicative of radiation-generated current which flows through the sub-element due to the electric field across the depletion regions, and the distances between adjacent sub-elements are sufficiently small that regions between adjacent sub-elements are fully depleted by said depleted regions.
A disadvantage of a device as described in this application is that as a consequence of the galvanic connections with the sub-elements for deriving the corresponding output signals, the minority charge carriers generated in each sub-element upon radiation are instantly carried off, so that the potentials of the sub-elements remain practically equal to each other whereby blooming may rather rapidly occur. Blooming is known in the art, and is a saturation effect wherein excess charges caused by a localized overload diffuse or flow to neighbouring diodes and thereby cause false information signals, causing a spreading of a white area in the display. It is the aim of the present invention to provide a device of the kind described, that shows improved performance with respect to blooming.